The destruction of negative ions by laser photodetachment suddenly modifies the electron and negative ion densities in a localized region. The subsequent recovery of negative ion density n−(t) may be measured with a second photodetaching laser pulse. These measurements, compared with a ballistic model for n−(t), are the basis of a negative ion temperature diagnostic, which is being developed and employed in H− and D− sources. In this paper the accompanying plasma potential perturbation and its effect on the negative ion response is discussed. The perturbation can introduce an error in negative ion temperature measurements. Late in time, the negative ion density is observed to recover more slowly than indicated by the ballistic theory. An intriguing mechanism is proposed for the late slow recovery of negative ion density, based on a small lingering potential perturbation and a hole in negative ion velocity space. These different theoretical approaches are illustrated with a detailed analysis of an example case from a hydrogen discharge.
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